I've been catching up on a few of the threads here and what Spatial Audio has been up to lately, and I see the concerns raised here.
There is very little substantive information about the new products like the S4 and S6, and where the website might talk about Spatial Audio's use of open baffle designs, it just says "For a detailed explanation of how dipole speakers differ from traditional monopole (box) speakers, we invite you to read an article by audiophile legend Paul McGowan here." And the link goes nowhere.
Spatial Audio used to speak for hours on podcasts and YouTube videos walking potential customers through the theory and benefits of their loudspeaker designs: they exhibited thought leadership (while properly crediting innovators on whose work they built, like Linkwitz).
With the new models, it's fairly mysterious. The S-series seems to be the M-series with a new mid/tweeter due to parts availability. However, the crossover frequency has changed, understandably. How much has the crossover changed? What is meant by "our new "Linear Drive" design topology"? Did the crossover move from point-to-point wiring to a circuit board? What advantages does the new tweeter have other than availability? Are the two 12" drivers the same as those used on the previous M4? Is the S-series painted ultralam or MDF? I assume MDF.
Why not send a pair to Erin's Audio Lab? The sparse info on the website says the S4 has succeeded in "minimizing directivity errors and maintains consistent output both on and off axis." This would show up on a Klippel measurement. The website also says the speaker is 4 ohms nominal, but what is the impedance plot in relation to the phase plot?
I'd like Spatial Audio to succeed. A significant attraction was the detail of technical information available via the forum, interviews, and reviews and the clear understanding of how and why they are innovating. Times have changed, however. That flow of information is a necessary but not sufficient condition. You can now go to Spinorama.org and see detailed measurements on hundreds of speakers. Pure Audio Project has become more visible and well-reviewed, competing with Spatial Audio among people looking for open baffle designs.
Maybe my perspective is misinformed, but I don't seem to be alone in raising concerns.